The following relates generally to wireless communication, and more specifically to channel reservation techniques for unlicensed spectrum.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems. A wireless multiple access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
Some wireless communications systems may operate using a first radio access technology (RAT), such as Long Term Evolution (LTE), and may include a number of base stations, each simultaneously supporting communications with multiple UEs. A second wireless communications multiple access system may operate according to a second RAT, e.g. Wi-Fi (e.g., IEEE 802.11), that may include a number of access points (APs) supporting communication with multiple stations in a shared frequency spectrum.
In some cases base stations and UEs, operating according to a first RAT may communicate in a shared or unlicensed radio frequency (RF) spectrum. APs and stations operating according to another RAT, for example Wi-Fi, may also operate in overlapping areas using the same unlicensed RF spectrum. The Wi-Fi devices may be able to contend with other Wi-Fi devices for access to a contention-based channel of the unlicensed RF spectrum according to established Wi-Fi contention protocols. For example the Wi-Fi devices may use IEEE 802.11 request to send (RTS)/clear to send (CTS) procedures. The RTS/CTS procedures may use certain control frames that have established control frame formats, for example, RTS, CTS, and/or CTS-to-self control frames. However, base stations and UEs using the first RAT and attempting to communicate using the unlicensed RF spectrum may not be able to effectively contend for access to the contention-based channel using these existing procedures. Thus, control frames or other control transmissions used to contend for the contention-based channel may not be understandable between a base station and/or UE and a Wi-Fi device. For example, the base stations and UEs may communicate using a different or larger channel bandwidth than the Wi-Fi devices. Where the base stations and/or UEs, as well as the Wi-Fi devices, are not able to effectively communicate in the same unlicensed RF spectrum without frame collisions, communications may be delayed, increasing communications latency.
Even where base stations and UEs operate according to the same RAT, a mechanism to contend for a contention-based channel may be desirable when transmitting in an unlicensed RF spectrum, for example to reduce frame collisions introduced by the hidden nodes problem (e.g., wireless nodes that are close to a receiver, but out of range from a transmitter) introduced by neighboring base stations and/or UEs that may transmit during the same time using the same shared or unlicensed RF spectrum. Unlicensed spectrum generally refers to spectrum available for use without a license and is typically subject to technical rules regarding access and transmitted power. Shared spectrum generally refers to spectrum that is licensed to one or more operators but follows some device coexistence procedures (e.g., a licensed radio frequency spectrum band having more than one licensed operator, a licensed radio frequency spectrum band having a prioritized operator, but providing for opportunistic sharing of resources, etc.).